In recent years, demands for an apparatus capable of performing irradiation of artificial light (artificial sunlight, pseudo-sunlight) similar to sunlight have been increasing. In particular, accompanying rapid development and diffusion of a solar cell technology, there arise demands for an apparatus capable of performing irradiation of very exact artificial sunlight that can be suitably used for testing, measurement, and experiment of a solar cell.
A key requirement which the artificial sunlight is required to satisfy is to have a light emission spectral close to natural sunlight. For satisfying this requirement, first, an attempt is made to obtain, as artificial sunlight, light that is from an incandescent light bulb and that has passed through a filter of some kind. One example of such a technique is disclosed in Patent Literature 1. According to the technique of Patent Literature 1, a water filter is provided in a light path of light from an incandescent filament lamp, so as to sufficiently improve proximity of spectral distribution of the light to spectral distribution of incandescent sunlight.
However, the technique of Patent Literature 1 has a problem such that an apparatus for this technique indispensably requires a mechanism of a complex optical system. Therefore, an apparatus performing irradiation of artificial sunlight by use of a simpler optical system has been developed. One example of such a technique is disclosed in Patent Literature 2.
According to the technique of Patent Literature 2, there is an optically open box frame below a surface for irradiating a solar cell. This box frame is partitioned so as to form neighboring discrete chambers that are optically independent and that respectively have upper surfaces optically open. Then, the respective chambers are provided with a halogen lamp and a xenon lamp together with respective reflector plates for adjusting uneven illumination. The reflector plates are provided on respective backsides of the halogen lamp and the xenon lamp facing respective open sections of the chambers. In addition, the open sections are provided with an optical filter exclusive for the halogen lamp and an optical filter exclusive for the xenon filter, respectively. In this configuration, irradiation of artificial sunlight is performed from underneath on a light-receiving surface of an object to be measured, by use of light obtained by turning on the halogen lamp and the xenon lamp.